The present invention relates to acetylene derivatives of the formula I 
in which
R is an alkyl or alkenyl radical having 1 to 15 carbon atoms which is unsubstituted, mono-substituted by CN or CF3 so at least monosubstituted by halogen, where, in addition, one or more xe2x80x94CH2xe2x80x94 groups in these radicals may be replaced, in each case independently of one another, by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, 
xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94 or xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 in such a way that O atoms are not linked directly to one another,
A1 and A2 are each, independently of one another,
(a) a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
(b) a 1,4-phenylene radical, in which, in addition, one so two CH groups may be replaced by N,
(c) trans-1,4-cyclohexenylene,
(d) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
where the radicals (a) to (c) may be monosubstituted or disubstituted by fluorine or CH3,
Z1, Z2 
and Z3 are each, independently of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94CH2CH2xe2x80x94 or a single bond,
m is 0, 1 or 2,
n is 0 or 1,
L1, L2 
and L3 are each, independently of one another, H or F, and
Y is xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CFxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CFxe2x80x94 or xe2x80x94CFxe2x95x90CFxe2x80x94,
with the proviso that, in the case where
Y=xe2x80x94Cxe2x89xa1Cxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94,
a) n=1 and Z3 is a single bond
or
b) L1 and/or L2 is/are fluorine
or
c) R is alkenyl or alkenyloxy having 2 to 12 carbon atoms
or
d) A2 is a pyridine radical, a pyrimidine radical or a trans-1,4-cyclohexylene radical which is monosubstituted or disubstituted by fluorine or CH3 
or
e) one of the radicals Z1, Z2 or Z3 is xe2x80x94COxe2x80x94Oxe2x80x94.
The invention furthermore relates to the use of these compounds as components of liquid-crystalline media, and to liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.
The compounds of the formula I can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases or the effect of dynamic scattering.
The invention has the object of finding novel, stable, liquid-crystalline or mesogenic compounds which are suitable as components of liquid-crystalline media and in particular simultaneously have comparatively low viscosity and relatively high dielectric anisotropy.
It has now been found that compounds of the formula I are eminently suitable as components of liquid-crystalline media. In particular, they have high xcex94∈ values at the same time as high clearing points. They can be used to obtain stable liquid-crystalline media having a broad mesophase range and advantageous optical and dielectric anisotropy values. These media furthermore have very good low-temperature behaviour.
Compounds of the formula 
are disclosed, for example, in JP 55-149371, JP 55-009012, JP 55-011529, PL 137 995 and PL 138 286.
Cyanoethyne derivatives of the formula 
are disclosed in JP 59-190 958 A2, JP 60-169 455 A2, JP 60-188 358 A2 and JP 60-019 756 A2.
Biphenylacetylenes of the formula 
are described in DE 32 46 440 A1.
However, the fluorinated compounds according to the invention are not mentioned therein.
However, in view of the extremely wide variety of areas of application of such compounds of high xcex94∈, it was desirable to have available further compounds of high nematogeneity which have properties which are precisely customized to the particular applications.
In addition, the provision of compounds of the formula I very generally considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquid-crystalline mixtures.
The compounds of the formula I have a broad range of applications. Depending on the choice of substituents, these compounds can be used as base materials of which liquid-crystalline media are predominantly composed; however, compounds of the formula I can also be added to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimize its threshold voltage and/or its viscosity.
In the pure state, the compounds of the formula I are colorless and generally form liquid-crystalline mesophases in a temperature range which is favourably located for electro-optical use. The compounds according to the invention are stable chemically and thermally.
The invention thus relates to the compounds of the formula I and to the use of these compounds as components of liquid-crystalline media. The invention furthermore relates to liquid-crystalline media comprising at least one compound of the formula I, and. to liquid-crystal display elements, in particular electro-optical display elements, which contain media of this type.
For reasons of simplicity, A4 and A3 below denote a radical of the formula 
and 
respectively, Cyc denotes a 1,4-cyclohexylene radical, Che denotes a 1,4-cyclohexenylene radical, Dio denotes a 1,3-dioxane-2,5-diyl radical, Dit denotes a 1,3-dithiane-2,5-diyl radical, Phe denotes a 1,4-phenylene radical, Pyd denotes a pyridine-2,5-diyl radical, Pyr denotes a pyrimidine-2,5-diyl radical and Bi denotes a bicyclo[2.2.2]octylene radical, where Cyc and/or Phe may be unsubstituted or monosubstituted or disubstituted by F or CN.
A1 and A2 are preferably selected from the group consisting of Cyc, Che, Phe, Pyr, Pyd and Dio.
Accordingly, the compounds of the formula I include bicyclic compounds of the sub-formulae Ia and Ib:
tricyclic compounds of the sub-formulae Ic to Ig
and tetracyclic compounds of the sub-formulae Ih to Ik:
Y is preferably xe2x80x94Cxe2x89xa1Cxe2x80x94, furthermore xe2x80x94CFxe2x95x90CFxe2x80x94 or xe2x80x94CFxe2x95x90CHxe2x80x94. Preference is also given to compounds of the formula I and of all sub-formulae in which A1, A2, A3 and/or A4 are 1,4-phenylene which is monosubstituted or disubstituted by F. In particular, these are 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and 3,5-difluoro-1,4-phenylene.
A1 and A2 are preferably 
Z1, Z2 and Z3 are preferably a single bond, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94 or xe2x80x94CH2CH2xe2x80x94, secondarily preferably xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CH2Oxe2x80x94 or xe2x80x94OCH2xe2x80x94. If one of the radicals Z1, Z2 and Z3 is xe2x80x94(CH2)4xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94CH2CH2xe2x80x94, the other radical Z1 or Z2 or Z3 (if present) is preferably a single bond.
m and n are preferably 1 or 0, particular preference being given to compounds in which m=n=0, furthermore those in which m+n=1.
If R is an alkyl radical and/or an alkoxy radical, this can be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.
Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.
If R is an alkyl radical in which one xe2x80x94CH2xe2x80x94 group has been replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it is in particular vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, or dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.
If R is an alkyl radical in which one xe2x80x94CH2xe2x80x94 group has been replaced by xe2x80x94Oxe2x80x94 and one has been replaced by xe2x80x94COxe2x80x94, these are preferably adjacent. These thus contain, an acyloxy group xe2x80x94COxe2x80x94Cxe2x80x94 or an oxycarbonyl group xe2x80x94Oxe2x80x94COxe2x80x94. These are preferably straight-chain and have 2 to 6 carbon atoms.
Accordingly, they are in particular acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.
If R is an alkyl radical in which one xe2x80x94CH2xe2x80x94 group has been replaced by unsubstituted or substituted xe2x80x94CHxe2x95x90CHxe2x80x94 and an adjacent xe2x80x94CH2xe2x80x94 group has been replaced by xe2x80x94COxe2x80x94 or xe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94Oxe2x80x94COxe2x80x94, this can be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Accordingly, it is in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.
If R is an alkyl or alkenyl radical which is monosubstituted by CN or CF3, this radical is preferably straight-chain, and the substitution by CN or CF3 is in the xcfx89-position.
If R is an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain, and halogen is preferably F or Cl. In the case of polysubstitution, halogen is preferably F. The resulting radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the xcfx89-position.
Compounds of the formula I which have wing groups R which are suitable for polymerization reactions are suitable for the preparation of liquid-crystalline polymers.
Compounds of the formula I containing branched wing groups R may occasionally be of importance owing to. better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components of ferroelectric materials.
Compounds of the formula I having SA phases are suitable, for example, for thermally addressed displays.
Branched groups of this type generally contain not more than one chain branch. Preferred branched radicals R are isopropyl, 2-butyl (=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy and 1-methylheptoxy.
If R is an alkyl radical in which two or more xe2x80x94CH2xe2x80x94 groups have been replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94COxe2x80x94Oxe2x80x94, this can be straight-chain or branched. It is preferably branched and has 3 to 12 carbon atoms. Accordingly,, it is in particular biscarboxymethyl, 2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-bis-carboxydecyl, bis(methoxycarbonyl)methyl, 2,2-bis-(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl)propyl, 4,4-bis(methoxycarbonyl)butyl, 5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)hexyl, 7,7-bis(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)-octyl, bis(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)-ethyl, 3,3-bis(ethoxycarbonyl)propyl, 4,4-bis (ethoxycarbonyl)-butyl or 5,5-bis(ethoxycarbonyl)hexyl.
Compounds of the formula I which have wing groups R which are suitable for polycondensation reactions are suitable for the preparation of liquid-crystalline. polycondensates.
The formula I covers the racemates of these compounds and the optical antipodes, and mixtures thereof.
Of the compounds of the formula I and of the sub-formulae, preference is given to those in which at least one of the radicals present therein has one of the preferred meanings indicated.
In the compounds of the formula I, preference is given to those stereoisomers in which the Cyc and piperidine rings are trans-1,4-disubstituted. Those of the abovementioned formulae which contain one or more Pyd, Pyr and/or Dio groups in each case include the two 2,5-positional isomers.
Preferred smaller groups of compounds are those of the sub-formulae I1 to I37:
Particularly preferred compounds are those of the sub-formulae I1, I2, I3, I4, I5, I8, I11, I13, I16, I21, I30, I31, I33, I34, I35, I36 and I37.
In the sub-formulae I1-I37, Y is preferably xe2x80x94Cxe2x89xa1Cxe2x80x94 or xe2x80x94CFxe2x95x90CFxe2x80x94, furthermore xe2x80x94CFxe2x95x90CHxe2x80x94. R is preferably straight-chain alkyl, alkoxy, 1-E- or 3-E-alkenyl having up to 6 carbon atoms, furthermore 2-Z-alkenyl, 4-alkenyl or alkenyloxy.
For the purposes of the present invention, the term xe2x80x9c1-E-alkenylxe2x80x9d covers radicals such as vinyl, 1-E-propenyl, 1-E-butenyl, 1-E-pentenyl, 1-E-hexenyl, 1-E-heptenyl, 1-E-octenyl, 1-E-nonenyl and 1-E-decenyl. The term xe2x80x9c2-Z-alkenylxe2x80x9d covers radicals such as allyl, 2-Z-butenyl, 2-Z-pentenyl, 2-Z-hexenyl, 2-Z-heptenyl, 2-Z-octenyl, 2-Z-nonenyl and 2-Z-decenyl. The term xe2x80x9c3-E-alkenylxe2x80x9d covers radicals such as 3-E-butenyl, 3-E-pentenyl, 3-E-hexenyl, 3-E-heptenyl, 3-E-octenyl, 3-E-nonenyl and 3-E-decenyl. The term xe2x80x9c4-alkenylxe2x80x9d covers radicals such as 4-pentenyl and the E- and/or Z- form of 3-hexenyl, 4-heptenyl, 4-octenyl, 4-nonenyl and 4-decenyl.
The term xe2x80x9calkenyloxyxe2x80x9d denotes alkenyloxy groups in which the oxygen is directly linked to a saturated carbon atom (i.e. groups having one or more carbon atoms between the double bond and the oxygen atom), such as (2-E-alkenyl)oxy, (3-alkenyl)oxy, (4-alkenyl)oxy, (5-alkenyl)oxy and the like. The term xe2x80x9c(2-E-alkenyl)oxyxe2x80x9d here covers radicals such as allyloxy, (2-E-butenyl)oxy, (2-E-pentenyl)oxy, (2-E-hexenyl) oxy, (2-E-heptenyl)oxy, (2-E-octenyl)oxy, (2-E-nonenyl)oxy and (2-E-decenyl)oxy. The term xe2x80x9c(3-alkenyl)oxyxe2x80x9d covers radicals such as (3-butenyl)oxy and the E- and/or Z-form of (3-pentenyl)oxy, (3-hexenyl)oxy, (3-hepentyl)oxy, (3-octenyl)oxy, (3-nonenyl)oxy and (3-decenyl)oxy. The term xe2x80x9c(4-alkenyl)oxyxe2x80x9d covers radicals such as (4-pentyl)oxy and the E- and/or Z- form of (4-hexenyl)oxy, (4-heptenyl)oxy, (4-octenyl)oxy, (4-nonenyl)oxy and (4-decenyl)oxy. The term xe2x80x9c(5-alkenyl)oxyxe2x80x9d covers radicals such as (5-hexenyl)oxy and the E- and/or Z-form of (5-heptenyl)oxy, (5-octenyl)oxy, (5-nonenyl)oxy and (5-decenyl)oxy.
It is self-evident to the person skilled in the art that claim 1 likewise covers all compounds of the formula I in which the H, N, O, C and F atoms have been replaced by their isotopes.
The 1,4-cyclohexenylene group preferably has the following structures: 
The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and are suitable for said reactions.
Use can also be made here of variants which are known per se, but are not mentioned here in greater detail. 
Preferred compounds are prepared, for example, as follows: 
The liquid-crystalline media according to the invention preferably comprise from 2 to 40 components, in particular from 4 to 30 components as further constituents besides one or more compounds according to the invention. These media very particularly preferably comprise from 7 to 25 components besides one or more compounds according to the invention. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenyl or cyclohexyl cyclohexylbenzoates, phenyl or cyclohexyl cyclohexylcyclohexanecarboxylates, cyclohexylphenyl benzoates, cyclohexanecarboxylates and cyclohexylcyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexylbenzenes, 4,4xe2x80x2-biscyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes, 1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.
The most important compounds suitable as further constituents of media according to the invention can be characterized by the formulae 1, 2, 3, 4 and 5:
In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are in each case, independently of one another, a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexylene, 1,4-cyclobexenylene, preferably trans-1,4cyclobexylene. Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl and G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and E are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.
In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x2 and Rxe2x80x3 are in each case, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are labelled with the sub-formulae 1a, 2a, 3a, 4a and 5a. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.
In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, which is known as group B, Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS or xe2x80x94(O)iCH3xe2x88x92(k+1)FkCl1, where i is 0 or 1, and k+1 is 1, 2 or 3; the compounds in which Rxe2x80x3 has this meaning are labelled with the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS, xe2x80x94CF3, xe2x80x94OCHF2 or xe2x80x94OCF3.
In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.
In a further smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x3 is xe2x80x94CN; this sub-group is referred to below as group C, and the compounds of this sub-group are correspondingly described by sub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1c, 2c, 3c, 4c and 5c, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkoxy or alkenyl.
In addition to the preferred compounds of groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the proposed substituents are also customary. All these substances are obtainable by methods which are known from the literature or analogously thereto.
Besides compounds of the formula I according to the invention, the media according to the invention preferably comprise one or more compounds selected from group A and/or group B and/or group C. The proportions by weight of the compounds from these groups in the media according to the invent;on are preferably
Group A: from 0 to 90%, preferably from 20 to 90%, in particular from 30 to 90%
Group B: from 0 to 80%, preferably from 10 to 80%, in particular from 10 to 65%
Group C: from 0 to 80%, preferably from 5 to 80%, in particular from 5 to 50%,
the sum of the proportions by weight of the group A and/or B and/or C compounds present in the particular media according to the invention preferably being from 5 to 90% and in particular from 10 to 90%.
The media according to the invention preferably comprise from 1 to 40%, particularly preferably from 5 to 30%, of compounds according to the invention. Further preferred media are those which comprise more than 40%, in particular from 45 to 90%, of compounds according to the invention. The media preferably comprise three, four or five compounds according to the invention.
The media according to the invention are prepared in a manner which is customary per se. In general, the components are dissolved in one another, expediently at elevated temperature. By means of suitable additives, the liquid-crystalline phases can be modified in accordance with the invention in such a manner that they can be used in all types of liquid-crystal display elements which have been disclosed hitherto. Additives of this type are known to those skilled in the art and are described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, it is possible to add pleochroic dyes for the production of colored guest-host systems, or substances for the modification of the dielectric anisotropy, the viscosity and/or the orientation of the nematic phases.
In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by acronyms, the transformation into chemical formulae taking place as in Tables A and B below. All the radicals CnH2n+1 and CmH2m+1 are straight-chain alkyl radicals containing n and m carbon atoms respectively. The coding in Table B is self-evident. In Table A, only the acronym for the parent structure is given. In individual cases, the acronym for the parent structure is followed, separated by a hyphen, by a code for the substituents R1, R2, L1 and L2:
The invention likewise relates to liquid-crystalline mixtures comprising at least one component of the formula I and preferably at least one further component selected from Tables A and B.
The examples below are intended to illustrate the invention without representing a limitation. Above and below, percentage data are per cent by weight. All temperatures are given in degrees Celsius. m.p. denotes melting point, c.p.=clearing point. Furthermore, C=crystalline state, N=nematic phase, S=smectic phase and I=isotropic phase. The numbers between these symbols indicate the conversion temperatures. xcex94n denotes optical anisotropy (589 nm, 20xc2x0 C.), xcex94∈ denotes the dielectric anisotropy [20xc2x0 C., 1 kHz], and the flow viscosity (mm2/sec) was determined at 20xc2x0 C.
xe2x80x9cConventional work-upxe2x80x9d means that water is added if necessary, the mixture is extracted with dichloromethane, diethyl ether, methyl tert-butyl ether or toluene, the organic phase is separated off, dried and evaporated, and the product is purified by distillation under reduced pressure or crystallization and/or chromatography. The following abbreviations are used: